In the treatment of visual acuity deficiencies, correction by means of eyeglasses or contact lenses is used by a large percentage of the population. Such deficiencies include patients having hyperopia or being far-sighted, myopia or near-sighted patients as well as astigmatisms caused by asymmetry of the patient's eye. More recently, to alleviate the burden of wearing eyeglasses and/or contact lenses, surgical techniques have been developed for altering the shape of the patient's cornea in an attempt to correct refractive errors of the eye. Such surgical techniques include photo-refractive keratectomy (PRK), LASIK (laser in-situ keratomileusis), as well as procedures such as automated lamellar keratectomy (ALK) or others. These procedures are intended to surgically modify the curvature of the cornea to reduce or eliminate visual defects. The popularity of such techniques has increased greatly, but still carries the risk in both the procedure itself as well as post-surgical complications.
An alternative to permanent surgical procedures to alter the shape of the cornea include orthokeratology, where a contact lens is applied to the eye to temporarily alter the shape or curvature of the cornea by mechanical reshaping of the corneal surface imparted by the lens. The reshaping of the cornea in orthokeratology has been practised for many years, but typically has required an extensive period of time to reshape the cornea.
Whilst orthokeratology lenses (orthokeratology lenses) have been used for many years, the manner in which such lenses operate, and in particular the physiology of the process of corneal reshaping, is still not fully understood. There is no consensus on the optimal shape for such lenses, and because no two eye shapes or refractive error parameters are the same, selecting an optimal lens shape for a particular patient is, at least to some extent, an intuitive rather than a prescriptive process.
Other corneal shaping techniques, such as those discussed above, also require a precise understanding of the optimal shape of the eye. It will be appreciated that, because differences of a few microns in thickness at different positions in the eye can make a significant difference to the efficacy of any treatment, an improved understanding of the optimal shape for any particular eye is considered to be important.
Typically, the treating of eyes to achieve improved vision using the techniques discussed above have concentrated on focusing light entering the eye along its axis, that is, from the point in space that the eye is ‘looking at’. However, it has recently been suggested that to control the progression of the refractive error it is not only important to optimally focus this central or axial light, but also to control the focus of light entering the eye at an angle, that is, coming from points in the visual space away from the direction the eye is ‘looking’—sometimes called peripheral vision. In optical engineering parlance, light rays travelling from points away from the direction of view of the eye are called off-axis rays, and the points in space representing peripheral vision is also called the mid-peripheral and peripheral field, and the ‘surface’ described by the collection of peripheral foci at the different peripheral field angles is called the curvature of field. The patent application, US 2005/0105047 (Smitth) discusses the importance of positioning peripheral, off-axis focal points, relative to the central, on-axis focal point for retarding or abating the progression of myopia or hypermetropia.
Thus, it will be apparent that a fairly wide region of the eye influences the long-term refractive state of the eye. Any process which reshapes the eye to correct only central field to achieve acute vision and yet ignores the effect that off-axis peripheral field light entering the eye may have, could potentially be damaging to its long-term refractive state. Thus, a treatment regime or process which produces an optimal shape over the whole optical surface of the eye is considered important.
Recent clinical studies have suggested a link between myopia control and the use of orthokeratology lenses in children. The inventors are aware of only three publications (as summarised below) that have addressed this issue.    1) Cho et al. (2005)            a. 2 year prospective pilot study with a historical control group        b. 7 to 12 year olds        c. 43 enrolled, 35 completed study        d. Difference in axial length and vitreous chamber depth between OK and control groups                    i. About 52% treatment effect in OK treated eyes                        e. Conclusions: OK can have both corrective and control effect in childhood myopia but there are substantial variations in changes in eye length among children and there is no way to predict the effect for individual subjects        f. Limitations: not randomized, no masking, no standard lens fitting protocol            2) Cheung et al (2004)            a. Case report: 13 year old Asian male examined over 2 years        b. Monocular OK treatment        c. Conclusions: eye with OK grew less than eye without treatment        d. Limitations: patient had uneven refractive errors to begin with and the eye without treatment may have been trying to “catch up” to the myopic eye        e. No control, case report            3) Reim (2003)            a. Retrospective case series        b. Only looked at change in refraction at 1 or 3 years after 3 months of stable OK wear        c. 253 subjects at 1 year, 164 subjects at 3 years        d. Conclusions: rate of myopia progression similar to GPs in Stone/Grosvenor/Koo study        e. Limitations: no controls, no axial growth measurements        
The only controlled study was the pilot conducted by Cho et al which still requires confirmation through a larger study. However, their findings suggest that orthokeratology may slow the growth of the eye but it does not work for all children. No one fully understands why orthokeratology gave a myopia control effect in only some of the children in that study.
To date, the inventors are not aware of any studies directed to the specific optics related to orthokeratology. Many have attempted to analyse the shape of the cornea via topographical analyses, but few have attempted to quantify and describe the exact corneal shape or profile for good vision (e.g. 6/6 vision), let alone myopia control.
US Patent Application 2005/0105047 (Smitth) describes optical intervention to control myopia progression. The publication discloses the optical ‘profile’ required to cease myopia growth and identified some techniques and devices which could be used. However, it has been determined that not all patients respond in the same way to treatment, and whilst some patients, for example, who undergo an orthokeratology treatment will show a slowing down or halting of myopia progression whilst they are receiving orthokeratology treatment, others will show that orthokeratology treatment has almost no effect on myopia progression.